An electrophotographic image forming apparatus includes a copying machine, a laser printer and other similar devices.
Usually there is a process cartridge in the electrophotographic image forming apparatus. The process cartridge can be mounted to a main assembly of the electrophotographic image forming apparatus and be demounted from the main assembly. For example, the process cartridge is prepared by integrally assembling a photosensitive drum and at least one of a developing means, a charging means, and a cleaning means as the processing means into a cartridge.
Current process cartridges include the following types: a first type of a process cartridge prepared by integrally assembling a photosensitive drum, and a developing means, a charging means and a cleaning means into a cartridge; a second type of a process cartridge prepared by integrally assembling a photosensitive drum and a charging means into a cartridge; and a third type of a process cartridge prepared by integrally assembling a photosensitive drum and two processing units consisting of a charging means and a cleaning means.
A user can mount the above process cartridge to the main assembly of an electrophotographic image forming apparatus in a detachable way. Therefore, the user can maintain the apparatus without relying on a service person. As a result, the user's operability of the maintenance of the electrophotographic image forming apparatus is improved. In the above conventional process cartridge, the mechanism used for receiving a rotational driving force from an apparatus main assembly to rotate a photosensitive drum is described as follows.
On a main assembly side, a rotatable member for transmitting a driving force of a motor and a non circular twisted hole, which is provided at a center portion of the rotatable member and has a cross section integrally rotatable with the rotatable member and provided with a plurality of corners, are provided.
On a process cartridge side, a non circular twisted projection, which is provided at one of longitudinal ends of a photosensitive drum and has a cross section provided with a plurality of corners, is provided. When the rotatable member is rotated in an engaged state between the projection and the hole in the case where the process cartridge is mounted to the apparatus main assembly, a rotational driving force of the rotatable member is transmitted to the photosensitive drum. As a result, the rotational force for driving the photosensitive drum is transmitted from the apparatus main assembly to the photosensitive drum. Another known mechanism is to drive a photosensitive drum by engaging a gear fixed to the photosensitive drum thus to drive a process cartridge consisting of the photosensitive drum.
However, in the conventional constitution described in U.S. Pat. No. 5,903,803, the rotatable member is required to be moved in a horizontal direction when the process cartridge is mounted to or demounted from the main assembly by being moved in a direction substantially perpendicular to an axial line of the rotatable member. That is, the rotatable member is required to be horizontally moved by an opening and closing operation of a main assembly cover. By the opening operation of said main assembly cover, the hole is separated from the projection. On the other hand, by the closing operation of the main assembly cover, the hole is moved toward the projection so as to be engaged with the projection. Accordingly, in the conventional process cartridge, a mechanism for moving the rotatable member in a rotational axis direction by the opening and closing operation of the main assembly cover is required to be provided to the main assembly. In the constitution described in U.S. Pat. No. 4,829,335, without moving the driving gear provided to the main assembly along the axial line direction thereof, the cartridge can be mounted to and demounted from the main assembly by being moved in a direction substantially perpendicular to the axial line. However, in this constitution a driving connection portion between the main assembly and the cartridge is an engaging portion between gears, so that it is difficult to prevent rotation non uniformity of the photosensitive drum.
U.S. Pat. App. Pub. No. US2008/0152388A1 discloses another type of the process cartridge. The improvement compared to the above process cartridge is to use a spherically universal joint driving-coupling structure as a driving component located at a longitudinal end of a photosensitive drum. This driving-coupling structure is easily disengaged from the driving component. Especially during a transportation process, this phenomenon occurs more easily, which causes the driving component to lose function and work unstably.